Manual back-focus adjustment on a Sony HVR-Z7U, using a 46in. Samsung LED TV to verify the results. (Click photo to enlarge.)
Photo D.W. Leitner

I began my last column with the question, What is auto back focus?

I compared depth of field to depth of focus and described the lens factors that impact both of them. I defined correct back focus as a function of precise lens mounting, accurate to within microns of spec. And I made the case that for any given angle-of-view, the smaller the sensor, the shorter the lens focal length—and therefore the less depth of focus available at the sensor surface.

Less depth of focus always means tighter tolerances in lens mounting, which is why 1/3in. camcorders are far less forgiving of back-focus errors than 2/3in. camcorders.

Ironic, isn’t it, that smaller, consumerish camcorders require tighter tolerances in lens mounting than larger 2/3in. cameras.

So, what is auto back focus? more